The broad objective of this proposal is the study of the mechanism and regulation of the process of differentiation of 3T3-L1 fibroblasts into adipocytes. Differentiation is the basic process by which specialized cells, tissues and organs are formed. Furthermore, cancer could be viewed at least phenotypically as a process of dedifferentiation. Since the direct effect of various stimuli and factors on the events of differentiation can be assessed in cell-culture systems, the 3T3-L1 fibroblastic subline will be used to study the process of covert and overt differentiation. The development of the enzymatic activities, structural proteins, membrane determinants (hormone receptors, surface antigens, glycoproteins), acidic nuclear proteins and m-RNA's characteristic of the adipose cell will be followed kinetically in an attempt to time the events leading to the appearance of the adipocytic pattern of metabolism. The influence of various hormones, and cyclic nucleotides on the process of differentiation will be investigated, and an attempt will be made to identify the loci of action and the nature of stimuli and controlling factors which switch on or off the various stages of differentiation. Separation of cells at different stages of differentiation will be achieved on the basis of either cell density or surface properties (surface antigens, hormone receptors) and affinity chromatography.